The Biomedical Research Institute has conducted preliminary studies on 26 anesthetized neonatal pigs hours old to 16 weeks of age which have indicated that nasal-;aryngeal-cardiorespiratory reflexes may be elicited by postural alterations, nasal obstruction and laryngeal manipulation leading to prolonged apnea, hypotension, bradycardia with A-V dissociation and death. These initial results have led to the consideration of infant pigs as an animal model for SIDS. The proposed work will be conducted in two phases with initial studies on anesthetized (pentobarbital) and/or lightly sedated pigs of various age groups subjected to nasal obstruction, postural alteration and laryngeal manipulation. Measurements will yield quantitative physiologic and biochemical data for evaluation and correlation of cardiorespiratory reflexes and autonomic nervous system maturity. The establishment of a high risk age group in which these reflexes are most prominent will be pursued utilizing autonomic blocking drugs, topical laryngeal anesthesia, and neurectomies to provide information concerning the mechanism(s) involved in these reflexes. The second phase will utilize induced acute hypoxemia by exposure to various concentrations of a N2- CO2-O2 gas mixture and surgically induced chronic hypoxemia to evaluate this condition as a predisposing factor to the development of reflex responses similar to those seen in human SIDS.